Acetaldehyde





Common name

acetaldehyde


IUPAC name

acetaldehyde


Systematic name

ethanal


Chemical formula

C2H4O


SMILES

CC=O


Molecular mass

44.05 g mol−1


Appearance

Colorless liquid
Pungent, fruity odor


CAS number

[75-07-0]


Properties


Density

0.788 g cm−3


Solubility in water

soluble in all proportions


Melting point

−123.5 °C


Boiling point

20.2 °C


Critical temperature

188 °C at 6.4 MPa


Viscosity

~0.215 at 20 °C


Structure


Molecular shape

trigonal planar (sp2) at C1
tetrahedral (sp3) at C2


Dipole moment

2.7 D


Hazards


MSDS

External MSDS


EU classification

Very flammable (F+)
Harmful (Xn)
Carc. Cat. 3


NFPA 704







4
2
2
 



R-phrases

R12, R36/37, R40


S-phrases

S2, S16, S33, S36/37


Flash point

−39 °C


Autoignition temperature

185 °C


RTECS number

AB1925000


Supplementary data page


Structure and
properties

n, εr, etc.


Thermodynamic
data

Phase behavior
Solid, liquid, gas


Spectral data

UV, IR, NMR, MS


Related compounds


Related aldehydes

Formaldehyde
 Propionaldehyde
 Ethylene oxide


Disclaimer and references


Acetaldehyde, sometimes known as ethanal, is an organic chemical compound with the formula CH3CHO (or MeCHO). It is a flammable liquid with a fruity smell. It occurs naturally in ripe fruit, coffee, and fresh bread and is produced by plants as part of their normal metabolism. It is perhaps best known as the chemical that causes "hangovers." In the chemical industry, acetaldehyde is used as an intermediate in the production of acetic acid, certain esters, and a number of other chemicals.

Contents

1 Ethenol
2 Applications in Organic Synthesis

2.1 Acetal Derivatives


3 Biological Aspects

3.1 Acetaldehyde and Hangovers


4 Other Occurrences
5 Safety
6 See Also
7 Notes
8 References
9 External Links
10 Credits



Ethenol
Traces of acetaldehyde exist in the enol form, ethenol, with Keq = 6 x 10-5.[1] Ethenol has been detected in the interstellar medium.

Applications in Organic Synthesis
Acetaldehyde is a common 2-carbon building block in organic synthesis.[2] Because of its small size and its availability as the anhydrous monomer (unlike formaldehyde), it is a common electrophile. With respect to its condensation reactions, acetaldehyde is prochiral. It is mainly used as a source of the CH3C+H(OH) synthon in aldol and related condensation reactions.[3] Grignard reagents and organolithium compounds react with MeCHO to give hydroxyethyl derivatives.[4] In one of the more spectacular condensation reactions, three equivalents of formaldehyde add to MeCHO to give pentaerythritol, C(CH2OH)4.[5]
In a Strecker reaction, acetaldehyde condenses with cyanide and ammonia to give, after hydrolysis, the amino acid alanine.[6] Acetaldehyde can condense with amines to yield imines, such as the condensation with cyclohexylamine to give N-ethylidenecyclohexylamine. These imines can be used to direct subsequent reactions like an aldol condensation.[7]
It is also an important building block for the synthesis of heterocyclic compounds. A remarkable example is its conversion upon treatment with ammonia to 5-ethyl-2-methylpyridine ("aldehyde-collidine”).[8]

Acetal Derivatives
Three molecules of acetaldehyde condense to form “paraldehyde,” a cyclic trimer containing C-O single bonds; four condense to form the cyclic molecule called metaldehyde.
Acetaldehyde forms a stable acetal upon reaction with ethanol under conditions that favor dehydration. The product, CH3CH(OCH2CH3)2, is in fact called "acetal," although acetal is used more widely to describe other compounds with the formula RCH(OR')2.[9]

Biological Aspects
In the liver, the enzyme alcohol dehydrogenase converts ethanol into acetaldehyde, which is then further converted into harmless acetic acid by acetaldehyde dehydrogenase. The last steps of alcoholic fermentation in bacteria, plants, and yeast involve the conversion of pyruvate into acetaldehyde by the enzyme pyruvate decarboxylase, followed by the conversion of acetaldehyde into ethanol. The latter reaction is again catalyzed by an alcohol dehydrogenase, now operating in the opposite direction.

Acetaldehyde and Hangovers
Most people of East Asian descent have a mutation in their alcohol dehydrogenase gene that makes this enzyme unusually effective at converting ethanol to acetaldehyde, and about half of such people also have a form of acetaldehyde dehydrogenase which is less effective at converting acetaldehyde to acetic acid. [10] This combination causes them to suffer from the alcohol flush reaction, in which acetaldehyde accumulates after drinking, leading to severe and immediate hangover symptoms. These people are therefore less likely to become alcoholics. The drug Antabuse (disulfiram) also prevents the oxidation of acetaldehyde to acetic acid, with the same unpleasant effects for drinkers. It has been used in the treatment of alcoholism.

Other Occurrences
Acetaldehyde is an air pollutant resulting from combustion, such as automotive exhaust and tobacco smoke, contributing to the addictive properties of tobacco.

Safety
Acetaldehyde is a toxin, an irritant, and a probable carcinogen.

See Also
Aldehyde
Acetic acid
Acetone
Formaldehyde
Notes

↑ Jerry March, Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (Wiley; 4 edition, 1992, ISBN 978-0471581482).

↑ Leo A. Paquette, David Crich,‎ Philip L. Fuchs,‎ and Gary A. Molander (eds.), Encyclopedia of Reagents for Organic Synthesis (Wiley, 2009, ISBN 978-0470017548). 

↑ Behrens, C., and Paquette, L.A., “N-Benzyl-2,3-Azetidinedione.” Organic Syntheses, Collected Volume 10. 2004, 41. 

↑ Walter, L.A., “1-(α-Pyridyl)-2-Propanol” Organic Syntheses, Collected Volume 3. 1955, 757. 

↑ Schurink, H. B. J., “Pentaerythritol.” Organic Syntheses, Collected Volume 1. 1941, 425. 

↑ Kendall, E.C., and McKenzie, B.F., “dl-Alanine.” Organic Syntheses, Collected Volume 1. 1941, 21. 

↑ Georg Wittig and A. Hesse, “Directed Aldol Condensations: β-Phenylcinnamaldehyde” Organic Syntheses, Collected Volume 6. 1988, 901. 

↑ R.L. Frank, F.J. Pilgrim, and E.F. Riener, “5-Ethyl-2-Methylpyridine” Organic Syntheses, Collected Volume 4. 1963, 451. 

↑ H. Adkins and B.H. Nissen, “Acetal” Organic Syntheses, Collected Volume 1. 1941, 1. 

↑  Q. Xiao, H. Weiner, and D.W. Crabb, “The Mutation in the Mitochondrial Aldehyde Dehydrogenase (ALDH2) Gene Responsible for Alcohol-Induced Flushing Increases Turnover of the Enzyme Tetramers in a Dominant Fashion.” J. Clin. Invest. 1996, 2027-2032. Retrieved April 3, 2018.


ReferencesISBN links support NWE through referral fees
March, Jerry. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure. Wiley; 4 edition, 1992. ISBN 978-0471581482
McMurry, John. Organic Chemistry. 6th ed. Belmont, CA: Brooks/Cole. 2004. ISBN 0534420052
Morrison, Robert T., and Boyd, Robert N. Organic Chemistry. 6th ed. Englewood Cliffs, NJ: Prentice Hall. 1992. ISBN 0136436692
Paquette, Leo A.,‎ David Crich,‎ Philip L. Fuchs,‎ and Gary A. Molander (eds.). Encyclopedia of Reagents for Organic Synthesis. Wiley, 2009. ISBN 978-0470017548
Solomons, T.W. Graham, and Fryhle, Craig B. Organic Chemistry. 8th ed. Hoboken, NJ: John Wiley. 2004. ISBN 0471417998
External Links
All links retrieved April 9, 2021.

National Institute for Occupational Safety and Health. NIOSH Pocket Guide to Chemical Hazards.

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